Generally speaking, a horizontal accumulator of such type comprises means controlling the running of the band, as a pulley block would, between fixed rollers and mobile rollers mounted on a wrap-around carriage which moves on a horizontal circulation track, along a longitudinal running axis, in order to form several superimposed portions running in opposite directions.
The band running forward, for instance, at lower level, passes on a return idler placed on a wrap-around carriage, comes back at higher level up to a fixed return idler placed at the upstream end of the track, in the running direction of the band, is fed forward again, passes over a return idler again mounted on another wrap-around carriage, is fed backward again onto a third level, and so on, whereas the band can be evacuated forward, while passing above the wrap-around carriage or, as is more often the case, backwards, to be directed toward a processing unit, for instance a pickling unit.
Inside the accumulator, the band forms therefore several superimposed portions running in opposite directions, respectively out and back on several spaced levels. For instance, in the layout according to the document U.S. Pat. No. 3,687,348, the band runs on six levels while passing over three return idlers. The idlers are situated on three different carriages, but it is possible, in other layouts, to use a single wrap-around carriage comprising several return idlers.
The length of accumulated band depends on the position of the wrap-around carriage on the circulation track and on the number of rollers supported by the carriage when a single carriage is used for several portions.
It is necessary to avoid any contact between the various portions of the band which run in opposite directions and this is the reason why the accumulator is connected to a plurality of intermediate supporting members, arranged along the circulation track of the carriage and carrying separating arms which extend horizontally, each on an intermediate level, between two running levels of the band.
However, the carriage should be allowed to come through in order to vary the length of accumulated band and it is why the supporting arms can pivot between a home position, parallel to the running axis, allowing the carriage to come through, and a working position for which the separating arm extends transversally between both running levels of the band.
Moreover, to reduce the moving masses and the cantilever length of the separating arms, the arms can advantageously be divided into two sections located on either side of the track and mounted respectively on two shafts provided along the track and installed to pivot each around a vertical axis. The pivoting of both shafts, respectively bringing the semi-arms home or extending them, is controlled by the displacement of the carriage on the track, in one direction or the other. For instance in the layout according to the document U.S. Pat. No. 3,687,348 or the document DE-A-2150759, each separating semi-arm is connected to a cam follower working together with a cam-operated device mounted on the carriage and whose profile has been determined to control the rotation of the separating arm around its shaft, in one direction or the other, according to the displacement direction of the carriage.
In the layout described in the document DE-A-2150759, each semi-arm supports a cam follower and is therefore substantially aligned with the band when the arms are closed. Consequently, the carriage supports two curved cams, each comprising a central inlet portion for the cam follower, this central portion being substantially aligned with the band and moving gradually away up to an outlet portion offset laterally in a position which matches complete opening of the arm.
Such a device does not enable to anticipate the time when the door opens since the said device solely starts to operate when the central portion of the carriage reaches the level of both separating semi-arms. Still, in modern units, the carriage moves at relatively high speed and, with the layout according to the document DE-A-2150759, there is a risk of violent impact against a door, which is not open yet or is open insufficiently.
For this reason, in the layout according to the document U.S. Pat. No. 3,687,348, both cam followers controlling the pivoting of each semi-arm are mounted respectively on either side of the track, each at the end of a control lever rotating integral together with the arm. Each cam follower working together with a cam provided on the wrap-around carriage side and which can extend cantilever towards the front section of the carriage over a distance enabling to anticipate the pivoting of the arm. However, the lateral frame supporting each cam is rather fragile and the cantilever distance is therefore somewhat minimal. Consequently, the anticipation time is too small for high carriage displacement velocities that may be reached in modern units.
Moreover, the ratio of the length that can be given to the cam in order to control the 90.degree. rotation of each semi-arm to the necessary lateral spacing is rather small and the double curvature of the cam is therefore relatively significant. There might be, at high velocities, risks of impact and, due to wear, increased clearances liable, in the long run, to cause material deterioration and too frequent stops of the production line.
Besides, untimely opening of the separating arms should be avoided in case of contact with the moving band.
Therefore, each separating arm must be connected with a locking device that, in the layout according to the document DE-A-2150759, is composed of a disk fitted with two notches corresponding, respectively, to the closed position and the open position of the arms, and into which may engage a lock that is mounted on a spring-loaded lever and working together itself with a second cam supported by the carriage. Thus, as soon as the cam follower engages into the first cam, the second cam controls the release of the lock which remains out of the way to enable the arm to rotate, whereas the lock engages into the second notch upon completion of the opening movement.
Still, clearances appear in the long run and the arm may unfortunately become unlocked, especially when the band runs at high speed, whereas an excessive load on the separating arm may cause untimely pivoting of the arm, thereby risking to make engaging with each other the portions of the band.
Besides, a synchronisation defect may generate damages and stop the unit in case of collision of the wrap-around carriage with a separating arm.
Moreover, as we have already stated, modern units operate at very high speed, whereby the carriage undergoes significant accelerations and it is therefore necessary to reduce, as far as possible, the inertia of the devices used for controlling the pivoting or the locking of the arms.
The aim of the invention is to obviate these various problems thanks to mechanism for controlling the rotation and the locking of the separating arms enabling the accumulator to operate in safety, whereas the mechanism used are particularly straightforward and of low inertia.